Microbial oil prospecting method



3,174,910 MICROBHAL OIL PROSPECTENG METHOD Donald G. Hitzman,Bartlesville, Okla, assignor to Phillips Petroleum Company, acorporation of Delaware No Drawing. Filed Nov. 14, 1962, Ser. No.237,732 4 Claims. (Cl. 195-4035) This invention relates to an improvedmethod of prospecting for deposits of hydrocarbons heavier than methaneby measuring the quantity of at least a second oxidizable gas, otherthan methane, oxidized simultaneously as the methane is consumed bybacteria in soil samples. In another aspect, it relates to a novelmethod of prospecting for oil in which the microbial action of pairs ofsamples of earth from each of a plurality of sample points are measuredfor the consumption of methane in one sample of each pair as compared tothe consumption of the same concentration of methane and a hydrocarbongas or gases heavier than methane in the other sample.

In the prior art, such as US. patent to Taggart, Jr., 2,349,472, May 23,1944, each soil sample was divided into two portions, one of which wasexposed to a methanecontaining atmosphere and the other to a heavierhydrocarbon gas-containing atmosphere. On page 2, column 1, lines 24-44,this patent states that by comparing the results obtained by the actionof the respective gases one can determine with certainty the amount ofbacteria contained in the soil sample which is propagated by heavierhydrocarbons. I have found, however, that there are many instance inwhich the method outlined by this patent is inoperative as a prospectingmethod to determine the presence or absence of hydrocarbons heavier thanmethane in some underground formations, because some organisms whichchiefly and preferably utilize methane may also use the higherhydrocarbon gases if no methane is present, so that confusion resultsbecause of consumption of the heavier hydrocarbon by the organisms thatnormally thrive on methane.

In the novel process of the present invention, the said confusion whichwould result in the process of said patent by the consumption of theheavier hydrocarbons by the organisms that normally thrive on methane isavoided by supplying respectively to each of a pair of soil samplestaken at the same point a first methanecontaining atmosphere to thefirst sample of each pair and a second methane-containing atmospherealso containing a heavier hydrocarbon gas to the second sample of eachpair, so that the organisms that normally and preferably thrive onmethane will consume the methane in both atmospheres, while theorganisms that normally thrive on heavier hydrocarbons will do so onlyin the atmosphere containing said heavier hydrocarbons. Then, bysubtracting the percent of total gas absorbed by the first sample ofeach pair from the first methane-con- EJMEW Patented Mar. 23, 1965taining atmosphere from the percent of total gas absorbed by the secondsample of each pair from the second heavier hydrocarbon andmethane-containing atmosphere of each pair of samples, a numerical valueis arrived at which eliminates the etfect of organisms which normallythrive on methane, and represents the amount of heavier hydrocarbonsconsumed by organisms which normally thrive on heavier hydrocarbons.

While a theoretical basis is not necessary to establish the presentinvention, it is believed wherever hydrocarbons heavier than methane areaccumulated by nature in underground formations, that small amounts ofthese heavier hydrocarbons will gradually leak out of storage and Worktheir way directly upward to the surface of the ground above the storagearea. the surface of the ground over both said areas storing saidheavier hydrocarbons and over areas which contain no heavierhydrocarbons, there is vegetable material present in the soil which isdecaying and partially breaking down into methane. The decay of thisvegetable material always produces methane, but will not producehydrocarbons heavier than methane. Microorganisms of all types have apower of spreading widely and are present in the soil, regardless ofwhether the soil is over a heavier hydrocarbon storage area or not. Butduring the years, microorganisms that normally thrive on hydrocarbonsheavier than methane will multiply and become concentrated in areasoverlying underground storage of hydrocarbons heavier than methane, andwill almost die out completely in areas which are not over suchunderground storage, because in the latter areas they never are suppliedany heavier hydrocarbons than methane. At the same time, organisms thatnormally thrive on methane will be present in any soil containingdecaying vegetation, whether the soil is over heavier hydrocarbonstorage areas or not, and therefore will be present in both types ofareas in large numbers. When a sample is exposed to an atmospherecontaining relatively large amounts of a specific hydrocarbon, theamount of the specific hydrocarbon consumed in a period of one to twoweeks is directly dependent on the concentration of microorganisms thatwill consume and thrive on that particular specific hydrocarbon. Also,said concentration of the specific microorganisms in the sample isdirectly dependent on the presence, 'or absence, of exposure of saidsample in situ in the ground over a large number of years to saidspecific hydrocarbon. The situation is complicated by the fact that inany area survey there is always a background value of methane, which maybe high or low depending on factors not relating to oil but to thingssuch as moisture, temperature, and mineral nutrients in the soil, whichfactors vary the amount of vegetation present and its rate of decay,which vegetation supplies organic matter which will decay to formmethane. Obviously, there is more methane in the soil in a swamp than ina desert region.

At the same time, near' feet being more preferred.

J The processes of the prior art have no means for distinguishing orallowing for this background value of methane.

By use of the present invention this variable background value, due todifferent amounts of methane in the swampy soil and in drier soil, issubstantially eliminated. By using pairs of samples from each point andexposing one set of samples to methane alone and the other set tomethane and heavier hydrocarbons, the background value due to themethane is canceled out.

One object of the present invention is to provide a novel and improvedprocess of microbial prospecting for oil or hydrocarbons heavier thanmethane.

Another object is to provide a novel microbial prospecting process inwhich the background effect of methane is eliminated and the results aredependent on the effect produced by hydrocarbons heavier than methane.

Another object is to provide an improved process of prospecting forhydrocarbons heavier than methane by measuring the quantity of a secondoxidizable gas other than methane, oxidized simultaneously as themethane is consumed by methane-consuming bacteria.

Numerous other objects and advantages will be apparent to those skilledin the art upon reading the accompanying specification and claims.

In practicing the present invention, soil samples are collected fromeach of a plurality of spaced sampling stations, as taught by my priorU.S. Patent 2,880,143 of March 31, 1959. The soil samples are preferablygathered below the level of surface contamination.

This patent states that depths from six inches to three feet are usuallypreferred, with depths from two to three In taking the samples, it isimportant that the soil sample be a sample of undisturbed soil at thedesired depth. One convenient method of sampling is to dig a hole withthe aid of an ordinary posthole digger to approximately the desireddepth and then,

by the use of a hand auger, take a sample of undisturbed soil from theside of the hole at the desired depth. The area under investigation isusually sampled according to a prearranged plot of said area. Obviously,any desired plot can be employed. While one sample at each samplingstation can be used in the practice of this invention, in order toreduce the possibility of a poor sample it is preferred to take twosamples at each station. Therefore, preferably at each sampling stationtwo holes spaced ten feet apart are dug and samples collected from eachhole. The samples are preferably placed in suitable sterile glasscontainers and suitably labeled to prevent confusion.

One hundred grams of soil from each of said two holes at each samplestation are blended to give a two hundred gram sample for each samplingstation. The two hundredgram sample of soil is then blended in a WaringBlendor or other suitable mixing device for approximately one minutewith one liter of a sterile mineral medium preferably having thefollowing composition:

Mineral medium N0. 1: Grams NH NO 1.0 MgSO 0.1 K HPO 0.5 CaSO 0.1

Distilled water to make 1 liter total.

The pH of the soil suspension is then adjusted to 7 while the suspensionis being agitated.

Mineral medium No. l is satisfactory if the samples treated with it willconsume gas from the first atmosphere containing only methane as itsonly hydrocarbon. If this does not occur, then other mineral mediumsshould be tried until one that will do so is found. However, it isextremely unlikely that any one of the three mineral mediums disclosedabove and below will ever fail to give good results in the practice ofthis invention.

The mineral medium which is used in preparing the above-described soilsuspensions and dilutions can be varied widely, as is well known tobacteriologists. Two other such mineral mediums which can be usedconsist of:

Mineral medium No. 2: Grams NH Cl 1.0 K HPO 0.5 MgNHAJPO4 CaSO 0.1Distilled water to make 1 liter total.

Mineral medium No. 3:

KNO 1.0 MgSO -7H O 0.2 KZHPOL 0.5 FeCl -6H O 0.05

Distilled water to make 1 liter total.

While the soil suspension is being agitated with the mineral medium, asample of about cc. is withdrawn by a hypodermic syringe and injectedinto an evacuated bottle, which has been scaled by a rubber gasket, byforcing the needle through the rubber gasket, discharging the contentsinto the bottle and removing the needle from the gasket, whereupon thehole in the rubber closes and the bottle retains its vacuum. The vacuumcan be established before or after adding the sample by withdrawing airthrough a hypodermic needle inserted and withdrawn in the same manner.The bottle should have a volume of about 200 cc. and should be filledabout half full of the soil sample slurry, leaving about 100 cc. spaceunder vacuum over the liquid slurry sample. After the soil suspensionhas been added, the bottle is filled with a selected gas mixturecontaining predetermined percentages of methane and air for one set ofsamples, and predetermined percentages of methane, air and one or moreheavier hydrocarbons, such as butane, propane or ethane, in the case ofthe other set of samples. The addition of the gas is also through ahypodermic needle inserted through the rubber gasket and then removedwith the rubber gasket closing the hole again. The gas mixtures can beenriched with oxygen and/ or carbon dioxide, but in the runs in Table Ionly air, methane and/ or propane was used. While ethylene, acetylene,propene, butene, butadiene and other unsaturated gaseous hydrocarbonsmay be used successfully in the practice of this invention, it ispreferred to use saturated paraffinic hydrocarbon gases 7 becauseconnate oil and heavier hydrocarbon gases are generally saturated innatural storage, and they are what the bacterial organisms have beenexposed to over the period of years that produced the population presentin the undisturbed sample of soil.

One way in which the pressure of gas in the sample bottles can beequalized immediately after the gas has been injected is to place allthe bottles in a water bath at the same temperature and bleed ofi anypressure over atmospheric by a hypodermic needle. Or the gas can beadded and its pressure measured and regulated at that time.

The sample and gas-containing bottles are incubated at room temperature(about 27 C.) and preferably started with atmospheric pressure'in thebottles (about 780 mm. of mercury absolute gas pressure). After one totwo weeks has passed (in TableI below, after 10 days), the pressure inthe bottles is either measured by pressure measurement through ahypodermic needle, or by allowing water to be drawn into the bottlethrough a hypodermic needle until the pressure inside is atmospheric andthen measuring the added volume of water by comparing liquid levelsbefore and after. The bottles can be graduated with a suitable volumericscale for the later purpose, such bottles being available on the marketand used by drug stores for medicine bottles. 0

TABLE I Sample values in percent of total gas absorbed after daysincubation at 27 C. and starting with 780 mm.

of mercury absolute gas pressure Content of Culture Armosphere AO SampleA B C BA (Process Point Type of Location (Present B-C of Invention)2,349,472) 20% CH4, 20% CH4, 20% 0 11 80% Air 20% CSHE, 80% Air 60% Air1 In Oil Field 32 10 17 22 5 d 8 29 21 9 -12 10. 5 24 9 13.5 15 1. 5 11.5 23 6 11.5 17 5. 5 7 17 10 10 7 -3 10. 5 27 20 7. 5 7 5 11 13 3 2 10 815 13. 5 5 -1. 5 8. 5 10 19. 5 20. 5 13 1 7.5 6.5 15 13 4 2 9 11 Inorder to compare the results of the process of the present inventionwith the process of U.S. Patent 2,349,- 472, cited above, in column 1,second paragraph, a series of triple samples was taken at 10 samplepoints, 1-10, at location intervals of 0.1 mile on a line running into aknown producing oil field from an area which had been tested by drillingoil wells which turned out to be dry holes. In that way, it waspositively known that sample points 1-4 should indicate the presence ofoil, whereas samples points 5-10 should only indicate the presence ofmethane from decaying vegetation. The three cultures using the same soilslurry of 250 gm. of soil to 1 liter of mineral medium #1 were preparedfor each soil sample. One hundred cc. of each culture was put into abottle having a volume of about 200 cc. and the remainder of the bottlewas charged with gas. In Table I above, bottles of Series A were chargedwith 20 percent methane and 80 percent air, while bottles of Series Bwere charged with 20 percent methane, 20 percent propane and 60 percentair, and bottles of Series C were charged with 20 percent propane and 80percent air. The bottles were incubated for ten days at about 27 C.(room temperature) and all the bottles started out with atmosphericpressure in the bottles. At the end of ten days, each bottle wasinverted and a hypodermic needle connected with a source of water Wasforced through a rubber gasket over the mouth of the bottle, allowingair pressure of the atmosphere to force water into the bottle until thepressure therein was atmospheric. From the change in liquid level thetotal amount of gas utilized by the bacteria or absorbed in the samplewas calculated as a percent of the original total amount of gas.

The values obtained in columns A, B and C were then subtracted to givethe values shown in columns B-A, B-C and A-C. Obviously, by subtractingthe values A from B in column B-A, the process of the present inventionis followed, Whereas if the values in column C are subtracted from thosein column A, as done in column A-C, the process of U.S. Patent 2,349,472(cited above) is being followed. It will be noted that only in columnB-A, the process of the present invention, is there consistently ahigher value for Samples 1-4 in the oil field than for Samples 5-10taken in the dry area. Only in the column of the present invention isthere no overlapping of values, and therefore only the present inventiondistinguishes between areas underlain by commercial amounts ofhydrocarbons heavier than methane from areas in which any wells drilledwould be dry holes.

Furthermore, it should be noted that in each of columns A, B and C takenalone, there is overlap between the values of Samples 14 in the oilfield and Samples 5-10 in the dry area, so no one of columns A, B and Calone would distinguish between the oil field and the dry area. 7

There are three ways in which two of columns A, B and C can be combined,namely, B-A of the present invention, A-C of U.S. Patent 2,349,472(cited above), and B-C which is not suggested by anyone. Of these threepossible ways, that of the present invention is the only one whichconsistently distinguishes between the values obtained in the oil fieldsamples and in the dry area samples, without over-lapping values.

While this invention has been described with reference to particularexamples given for illustrative purposes, 0bviously this invention isnot limited thereto.

Having described my invention, I claim:

1. A method for prospecting for petroleum deposits which comprisescollecting a plurality of samples of soil at each of a plurality ofpoints over an area under investiga tion, admixing a known portion ofeach of said samples with aqueous inorganic salt medium forhydrocarbon-consuming bacteria, subjecting at least one sample from eachpoint to the action of a first atmosphere consisting essentially of afree oxygen-containing gas and methane, subjeoting at least one othersample from the same point to the action of a second atmosphereconsisting essentially of a free oxygen-containing gas, an unsubstitutedhydrocarbon gas heavier than methane, and substantially the same amountof methane as in said first atmosphere, and comparing the amounts of thehydrocarbon gas heavier than methane taken up by the samples from thedifierent points exposed to said second atmosphere for a selected timein the range of about 1 to 2 weeks, after subtracting from the total gastaken up the amount of methane taken up by samples at the samerespective points exposed to said first atmosphere in about the sameselected time, to determine at which preferred points more hydrocarbongas heavier than methane was taken up as an indication of the likelypresence of petroleum deposits underneath said preferred points.

2. A method for prospecting for petroleum deposits which comprisescollecting a plurality of samples of soil at each of a plurality ofpoints over an area under investigation, admixing a known portion ofeach of said samples with aqueous inorganic salt medium forhydrocarbon-consuming bacteria, subjecting at least one sample from eachpoint to the action of a first atmosphere consisting essentially of afree oxygen-containing gas and methane, subjecting at least one othersample from the same point to the action of a second atmosphereconsisting essentially of a free oxygen-containing gas, a hydrocarbongas heavier than methane, and substantially the same amount of methaneas in said first atmosphere, and comparing the amounts of thehydrocarbon gas heavier than methane taken up by the samples from thedifferent points exposed to said second atmosphere for a selected timebetween about 1 and 2 weeks, after subtracting from the total gas takenup the amount of methane taken up by samples at the same respectivepoints exposed to said first atmosphere in about the same selected time,to determine at which preferred points more hydrocarbon gas heavier thanmethane was taken up as an indication of the likely presence ofpetroleum deposits underneath said preferred points.

3. A method for prospecting for petroleum deposits which comprisescollecting a plurality of samples of soil at each of a plurality ofpoints over an area under investigation, admixing a known portion ofeach of said samples with aqueous inorganic salt medium forhydrocarbonconsuming bacteria, subjecting at least one sample from eachpoint to the action of a first atmosphere consisting essentially of airand methane, subjecting at least one other sample from the same point tothe action of a second atmosphere consisting essentially of air, ahydrocarbon gas heavier than methane, and substantially the same amountof methane as in said first atmosphere, and comparing the amounts of thehydrocarbon gas heavier than methane taken up by the samples from thedifferent points exposed to said second atmosphere for a selected timebetween about 1 and 2 weeks, after substracting from the total gas takenup the amount of methane taken up by samples at the same respectivepoints exposed to said first atmosphere in about the same selected time,to determine at which preferred points more hydrocarbon gas heavier thanmethane was taken up as an indication of the likely presence ofpetroleum deposits underneath said preferred points.

4. A method for prospecting for petroleum deposits which comprisescollecting a plurality of samples of soil at each of a plurality ofpoints over an area under investigation, admixing a known portion ofeach of said samples with aqueous inorganic salt medium forhydrocarbonconsuming bacteria, subjecting at least one sample from eachpoint to the action of a first atmosphere consisting essentially of airand methane, subjecting at least one other sample from the same point tothe action of a second atmosphere consisting essentially of air,propane, and substantially the same amount of methane as in said firstatmosphere, and comparing the amounts of propane taken up by the samplesfrom the different points exposed to said second atmosphere for aselected time between about 1 and 2 weeks, after subtracting from thetotal gas taken up the amount of methane taken up by samples at the samerespective points exposed to said first atmosphere in about the sameselected time, to determine at which preferred points more propane wastaken up as an indication of the likely presence of petroleum depositsunderneath said preferred points.

References Cited in the file of this patent UNITED STATES PATENTS

1. A METHOD OF PROSPECTING FOR PETROLELUM DEPOSITS WHICH COMPRISESCOLLECTING A PLURALITY OF SAMPLES OF SOIL AT EACH OF A PLURALITY OFPOINTS OVER AN AREA UNDER INVESTIGATION, ADMIXING A KNOWN PORTION OFEACH OF SAID SAMPLES WITH AQUEOUS INORGANIC SALT MEDIUM FORHYDROCARBON-CON SUMING BACTERIA, SUBJECTING AT LEAST ONE SAMPLE FROMEACH POINT TO THE ACTION OF A FIRST ATMOSPHERE CONSISTING ESSENTIALLY OFA FREE OXYGEN-CONTAINING GAS AND METHANE, SUBJECTING AT LEAST ONE OTHERSAMPLE FROM THE SAME POINT TO THE ACTION OF A SECOND ATMOSPHERECONSISTING ESSENTIALLY OF A FREE OXYGEN-CONTAINING GAS, AN UNSUBSTITUTEDHYDROCARBON GAS HEAVIER THAN METHANE, AND SUBSTANTIALLY THE SAME AMOUNTOF METHANE AS IN SAID FIRST ATMOSPHERE, AND COMPARING THE AMOUNTS OF THEHYDROCARBON GAS HEAVIER THAM METHANE TAKEN UP BY THE SAMPLES FROM THEDIFFERENT POINTS EXPOSED TO SAID SECOND ATMOSPHERE FOR A SELECTED TIMEIN THE RANGE OF ABOUT 1 TO 2 WEEKS, AFTER SUBTRACTING FROM THE TOTAL GASTAKEN UP THE AMOUNT OF METHANE TAKEN UP BY SAMPLES AT THE SAMERESPECTIVE POINTS EXPOSED TO SAID FIRST ATMOSPHERE IN ABOUT THE SAMESELECTED TIME, TO DETERMINE AT WHICH PREFERRED POINTS MORE HYDROCARBONGAS HEAVIER THAN METHANE WAS TAKEN UP AS AN INDICATION OF THE LIKELYPRESENCE OF PETROLEUM DEPOSITS UNDERNEATH SAID PREFERRED POINTS.